Electronic amplifying apparatus



Sept. 29, 1953 0. w. RIVENBURG ELECTRONIC AMPLIF'YING APPARATUS 2Sheets-Sheet 1 Filed Aug. 21, 1950 Jnnentor DOUGLAS W. RIVENBURG P 1953D. w. RIVENBURG 2,654,057

ELECTRONIC AMPLIFYING APPARATUS Filed Aug. 21} 1950 2 Sheets-Sheet 2RELAY IN I RELAY OUT I RELAY IN lllllllllllllllllm 'II'IIIIIIIIIII'I'I3nmntor DOUGLAS W. RIVENBURG Gttorncg Patented Sept. 29, 1953 ELECTRONICAMPLIFYING APPARATUS Douglas W. Rivenburg, Minneapolis, Minn., as

signor to Minneapolis Company, Minneapolis,

Delaware -Honeywe1l Regulator Minn., a corporation of Application August21, 1950, Serial No. 180,662

6 Claims. 1

The present invention relates to electronic amplifier circuits andparticularly to an electronic amplifier circuit incorporating a phasediscriminator stage adapted for use in a system wherein a reversiblemotor is operated in accord ance with changes in the phase of an inputsignal.

Such an apparatus might well be used in a temperature controllingmechanism for a closed chamber in which a temperature responsive networkefiectively applies a control signal to the input of the amplifierdepending on the magnitude and direction of unbalance of the networkfrom a given control point. It is desirable that such an amplifiercircuit provide a means of preventing the controlled mechanism fromovershooting the desired position established by the controllingnetwork, thus, eliminating cycling about the established control pointposition which is commonly known as hunting.

Considerable difficulty has been experienced in some types of amplifiersas a result of the phase shift of the input signal with respect to thephase of a reference voltage on the motor. To elim i nate such phaseshift difliculties, A. C. discriminator stages have been added to suchamplifiers in which an A. C. voltage becomes a reference voltage in theamplifier and any phase shift of the input signal only reduces theelfectiveness of the signal, rather than cause possible faulty operation. In this type of amplifier under certain conditions thesensitivity of the amplifier is often reduced by the reverse flow ofelectrons in the electronic discharge devices used in the discriminatorstage when the anode reference voltage swings negative. This phenomenais more commonly known as back emission. In a discriminator stage havingat least two electron discharge devices forming two sections in whichthe control electrodes of the two sections are commonly connected, thereverse electron flow in one section can render small input signalsnearly ineffective in one and sometimes in both sections of the stage.

The present invention is arranged so that the back emission difiicultiesof the discriminator stage of the amplifier are eliminated and the A.reference voltage is retained in the discriminator stage. The inventionalso provides a simplified means for rendering the control signalperiodically ineffective, thereby causing intermittent operation of theload device to eliminate any hunting tendencies.

It is therefore an object of the invention to provide an amplifierhaving an improved discriminator stage wherein there is no backemission.

Another object of the invention is to provide an amplifier having animproved discriminator stage wherein an A. C. reference voltage is usedin the discriminator which is arranged to eliminate any reverse currentflowing tendencies of thecomponents of the stage.

Still another object of the invention is to provide an amplifier thathas an improved and simplified means to selectively render an inputsignal, that is intended to operate a load device, intermittently orcontinuously efifective depending on the magnitude of the input signal.

Another object of the invention is to provide an amplifier that has animproved and simplified means of changing the biasin circuit of suchamplifier so that a motor that is being controlled by a control networkindirectly through the amplifier can be operated continuously orintermittently in one direction of rotation or the other depending onthe magnitude and phase relation of the signal received from the controlnetwork.

Other objects and advantages of my invention will become apparent from aconsideration of the appended specification, and drawings, in which:

Figure 1 is an electrical wiring diagram of the amplifier and a controlsystem wherein the amplifier may be advantageously used,

Figure 2 is a graphical representation of the control signals andvoltages causing operation of the amplifier circuit shown in Figure 1.

Figure 1 Referring to Figure 1, my invention is shown to comprise anelectronic amplifier I0 which has a bridge network I I connected to aninput terminal I2 of the amplifier I0 and a reversible motor I3connected to output terminals I4 and I5 of the amplifier It. Theamplifier It) is operated from a source of alternating power that iscon- 1 nected to the power terminals I6 and Il The bridge network IIthat is connected to the input terminal I2 can be any type of bridgenetwork that produces a variable magnitude alternating signal in whichthe magnitude of the output signal of the network depends on theunbalance condition of the network, and the phase of the output signalof the network will depend on the direction of the unbalance of thebridge. The bridge network II comprises an upper left leg having avariable resistance element 23 and a slider 30 and a temperaturesensitive element I8, an upper right leg having a fixed resistanceelement 25, a lower left leg having a fixed resistance element 2?, and alower right leg having two temperature sensing elements I9 and 20, and afixed resistance element 26. A variable resistance element 28 isconnected between the lower extremities of the lower left and lowerright legs of the bridge network II and has a slider 3|. An alternatingpotential source, not shown, is

connected to the bridge H by means of two input terminals 32 and 33. Theinput terminal 32 connected between the upper left and lower left legsof the bridge ii and the input terminal 33 is connected between theupper right and lower right legs or" the bridge. An output terminal 3 ofthe bridge l is at the connection of the upper left and upper right legsof the bridge network and is connected to the input terminal 12 of theelectronic amplifier Iii by means of a conductor Another resistanceelement 41!, having a slider l! that is connected to ground by means or"a connection e2, which forms another output terminal for the bridge, isconnected to bridge H in parallel with the variable resistance element29. It is therefore obvious to those familiar with the art that if the.bridge network H becomes unbalanced a signal will appear at the outputterminals 34 and 42 of the bridge having a phase relation depending onthe direction of unbalance and a magnitude depending on the amount ofunbalance that exists.

The motor 83 is provided with two field windings M and st and a rotor43. One end of each of the motor windings M and 45 is connected to acommon ground terminal and the other ends of the two windings areconnected to the output terminals i l and i of the amplifier it. Acapacitor A 6 is connected between the two windings KM and 45 of themotor in such a manner that the capacitor is across the output terminalsi l and H5. The motor [3 is of the split phase type wherein alternatingpower is applied to one or the other of the two terminals it or I5 tocause the motor to run in one direction or the other. The motor rotor 33is mechanically coupled to a gear train A! which produces a reduction inthe angular movement of the output shaft of the motor. The output shaftof the gear train 41 is mechanically coupled to a second gear mechanismt8 and also to the slider arm ll of the bridge network H. The gearmechanism 68 is connected by means of a shaft 39 to a valve 50.Therefore, it is to be understood that the operation of the reversiblemotor I3 will control the position of the slider arm 4! on the bridgenetwork H and also change the output of the valve 55 In this particularcase the valve 50 can control the heat input to the chamber whosetemperature is being controlled by the temperature sensitive bridgenetwork II.

As stated above, the power is supplied by a source of power, not shown,connected to the power terminals to and ii. The grounded side of theinput power source is connected to the terminal !'J. The end terminalsof a primary winding 55 of a transformer 56 are connected to the powerterminalsifi and H. The primary winding 55 also has two taps 5'! and 58.The transformer 56 also comprises a secondary winding 59 having two endterminals 80 and El and a grounded center tap 62, and a second winding63 having two end terminals 84 and 65.

The electronic amplifier ill comprises three stages of amplification M,H and i2 and a discriminator stage '53 that is connected to the outputof the third stage of amplification 12. The first stage of amplificationH3 comprises a triode it which can be a commercial type tube such as asubminiature tube #5744, having an anode 15, a control electrode it, anda cathode H which is heated by a heater E8. The anode of the first stageof amplification i0 is supplied a positive unidirectional potential by apower supply is through a circuit that can be traced from the powersupply it, through a conductor 80, a plate resistor 85, a conductor 86,and to the anode 75. The output of the first stage of amplification itis connected to the input of the second stage H by means of a capacitor3? that will pass an alternating signal and not direct current.

The second stage of amplification H comprises a similar triode 33 havingan anode 39, a control electrode as, and a cathode 9! which is heated bya heater 92. The second stage of amplification H is also supplied aunidirectional potential from the power supply it by means of a circuitthat can be traced through a conductor 93, a plate resistor 94, and aconductor to the anode 89. The input circuit of the second stage ofamplification ii is connected to the control electrode 5a which isbiased in a con ventional manner by means of a negative D. C. potentialthat is obtained from a second power supply Hit through the circuit thatmay be traced from a conductor iti, a conductor M32, a bias resistor[03, and a conductor it i to the control electrode 9%. A feedbackresistor ltd is connected between the anodes i5 and as or the first twostages of amplification. This feedback resistor feeds back a portion ofthe voltage from the second stage of amplification thereby reducing theeffectiveness of the output of the first stage of amplification and alsoprovides an ainplifier circuit that has a greater stability and lesstendency of developing an internal oscillation.

The third stage of amplification 12 comprises another similar triode iit having an anode l i i, a control electrode H2, and a cathode H3 thatis heated by a filament ms. The output of the second stage ofamplification H is fed into the input circuit of the third stage ofamplification by means of a blocking capacitor lit and a resistor iii;and the circuit can be traced from the anode 89, through the capacitorH5, and resistor H6 to the control electrode iii. of the triode H0. Thevoltage drop across a grid limiting resistor H6 reduces the bias voltagebetween the control electrode H2 and ground should the input signal tothe third stage of amplification exceed a predetermined positive maximumvalue and a grid current flow between the control electrode H2 and thecathode H3 of the electronic discharge device lid. The anode Hi of thethird stage of amplification i2 is provided with a unidirectionalpositive potential from the power supply it through a circuit that canbe traced from a conductor iii, through a resistor I i8 and a conductorE E9 to the anode i i. The input circuit of the third stage ofamplification 12 is provided with a negative bias voltage that issupplied from the power supply Mill through a circuit that can be tracedfrom a conductor ms, through a resistor i283, conductor I25 to a commonterminal connection 26 that is positioned between the condenser 5 i5 andthe resistor I [6, the latter being connected to the control electrodeH2. In the first three stages of amplification the cathodes of each ofthe three triodes are connected to ground as well as one of the two endterminals of each of the heaters 18, 92 and H4. The second end terminalof the three heater elements are connected to the tap 58 on the primarywinding 55 of the transformer 56.

The discriminator stage 13 comprises a discriminator tube 52! which isknown as the commercial miniature tube type #568? having two triodesections. The first section in the discriminator tube I21 comprises ananode I28, a control electrode I29, and a cathode I; and the secondsection comprises an anode I3I, a control. electrode I32, and a cathodeI133. The cathodes of the two sections of the discriminator tube I21 areheated by means of a heater elem nt I34 having two end connections, oneof which is connected to ground and the other being connected to the tap51 on the primary winding 55 of the transformer 56. The cathodes I30 andI33 of the discriminator tube I21 are connected to the end terminals 60and 6| of the secondary winding 59 of the transformer 56 by means oftheconductors I35 and I 36., respectively, to am ply a referencepotential on the cathodes or the discriminator stage such that thecathodes I30.

and I33 will be alternately and oppositely positive and negative withrespect to the center tan or ground terminal 62. The control electrodesI29 and I32 of the discriminator stage are com monly connected to theoutput of the third stage of amplification 12 by means of a couplingcapacitor I through a circuit that can be traced from the anode III,throu h a conductor H9. and a capacitor !40 to the control electrodes ofthe discriminator stage. A negative bias potential is supplied to thecontrol electrodes of the discriminator stage by the power supply I00 bya circuit that can be traced through a conductor I4I a filtering networkconsisting of the parallel combination of a resistor I42 and a capacitorI43. to the control electrodes of the discriminator tube I21. Anothersource of unidirectional potential of a positive value is supplied tothe anodes I28 and I3I of the discriminator stage from a power supplyI44. The circuit can be traced from the power supply I44, through theconductor I41, a relay assembly I45, and a conductor I 49 to the anodeI28; and from the conductor I41, a relay assembly I46, and conductor I48to the second anode I3I.

It is therefore obvious from the circuits that have been traced abovethat an input signal can be applied to the input terminal I 2 of theampli, fler I0 and be amplified by the three stages of amplificationbefore being applied to the input terminal of the discriminator stage ofthe ampli fier. The discriminator stage, as will be ex plained in moredetail below is effective to en! ergize one or the other of the tworelay asseme blies depending on the phase relation and magnitude of thereceived input signal.

The power supply 19 comprises a unidireca tional current conductor orrectifier I50, which may be of the selenium type oi rectifier. Thisrectifier is connected by means of a conductor I to the input powerterminal IS. The output of the rectifier I 50 is connected to a filterinnetwork comprising a resistor I56 and two capacitors I51 and I58. Thepower supply circuit 19 can be traced through the conductor I55, therectifier I 50, and conductor I53 that contains the junction ofconductors 93 and I I 1, to the parallel filter network comprising twolegs, one of which is the capacitor I58 connected to ground and theother is the series connection of the resistor I56 and the capacitor I51that is connected to ground, The conductor is connected to the powersup.- ply 19 at the junction of the resistor I56 and the condenser I51.

Th power supply I00 mprises a number of series connected resistors I60,I6I, I62 and I63 that are connected to a second unidirectional cur? rentconductor or rectifier I64. A circuit can be traced from the groundterminal through he resistor I60. the resistor IB the resistor I82, thejunction 01. conductor II, he resistor I63, the rectifier I 64, and theconductor I55 to the nput ower terminal IS. A ap tor 6 s placed from theground connection to the junction of the resistance I63 and therectifier I64.

The third power supply I44 is a voltage doubler circuit and comprisestwo unidirectional current conductors or rectifiers I10 and HI con-.nected in series in such a manner that a circuit can be traced from a rond term nal, th ou h the rectifier I10, the second rectifier I1I, theJunction of he conductor. I41, to a c pacito 12, and back to the groundconn ct on- Alte nat ing power for the supply I44 is obtained irom theinput terminal I6 through a circuit that can be traced through theconductor I55, and a capacitor I13 to a junction between the tworectlfiers I10 and HI.

In the power supply 19 when the alternating potential that is suppliedfrom the input terminal tors I51 and i 58 which smooths the voltage waveI6 is positive the rectifier i553 conducts current, pulse that chargesthe capa t rs I5 and I58 so that a positive direct current voltage isavailable at the anodes of the three stages of amplification 10, H and12. A resistance I56 is a component of the filtering network comprisingthe capacitors I51 and I 58 which smooths the voltage wave that isapplied to the first stage of amplification 10.

The rectifier I64 in the power supply I 00 is connected in such a mannerthat the voltage drop across the series resistors provides a negativesource of potential with respect to ground when measured at each of thevoltage taps. The capacitor I66 is placed across the series resistancenetwork to provide a filtering means to smooth out the half wave pulsesderived from the rectifier.

In the third pow supply I 4 wh n a n a v voltage of the negati vo tage ccle of a terna ing voltage available from terminal I6 is applied to thecapacitor I13 the capacitor is charged by a current flowing from ground.through the rectifier I 10. On the second half cycle of the alternatingvoltage when the voltage is positive a current will flow through therectifier I1I to charge the capacitor I12 to a value of voltageapproximately equal to the sum of the positive applied voltage and thevoltage across condenser I13. A voltage of approximately twice theapplied voltage from the alternating source is available at theconductor I41 and is applied to the discriminator stage 13.

The relay assemblies M5 and I46 each comprise two sets of blades andcontacts. The first relay assembly I45 has a first set of contactscomprising a movable blade I15 and a permanent contact I14; and a secondset of contacts comprising a permanent contact I 16 and the movableblade I11. The second relay assembly I46 also comprises a first set ofcontacts having a permanent contact I 19 and a movable blade I18; and asecond set of contacts having a permanent contact I8I and a movableblade I80. The relay of the relay assembly I 45 comprises a winding I 82that is shunted by a capacitor I83. Similarly constructed is the relayassembly I46 which comprises a winding I84 and a capacitor I85 shuntmthe Windin The contacts I 14 and I19 of the first set of contacts ofeach of the relay assemblies are connected to the conductor I55 which isconnected to the power supply input terminal I6. The movable blades I15and I18 of the two relay assemblies are connected to the outputterminals I4 and I5, respectively, of the amplifier I0. It is obviousfrom the connection that the direction of operation of the motor I3 willdepend on which of the relay assemblies I45 or I46 is energized. If therelay assembly I05 is energized the motor I3 will rotate in onedirection as a result of the phase relation of the current in thewindings M and 45. If the second relay assembly I45 is energized theoperation of the motor I3 will be in the opposite direction. It istherefore to be noted that the operation of the motor I3 depends onwhich section of the discriminator stage 13 conducts a current of asufficient magnitude to operate the relay assembly in the circuittherewith.

The second set of contact members of the two relay assemblies I05 andI46 have the permanent contacts 116 and IBI connected to the conductorI55 which, as stated before, is connected between the resistors iti and.i02 of the power supply I00. The movable blades Ill and E80 areconnected in common to a conductor I90 which is connected to a resistorIOI. The resistor I9I is connected to the junction I20 which is in thecontrol circuit of the third stage of amplification in such a manher asto make a circuit from the control electrode H2 of the amplificationstage 12, through the resistor IIB, junction I26, resistor I9I,conductor I90, parallel relay assembly, and conductor I65 to the powersupply I00. From the foregoing circuit it is obvious that if either ofthe two relay assemblies I05 or I46 should be energized the associatedcontacts I16 and III or IBI and I80, would operate to apply a bias fromthe power supply I00 to the control electrode II2.

The values set forth in the following table are provided to illustratemore completely the specific amplifier circuit which has beenconstructed to carry out the principles of my invention. It should beunderstood, however, that these values are provided by way of exampleonly, and that other values may be used without departing from myinvention.

Reference Numeral Quantity Suggest Value Resistance. 2.2 meg-ohms. do100,000 ohms. d0 470,000 ohms.

1.0 megohms. 1.5 megohms. 22 megohms. 33 megohms. 4.7 megohms. 100,000ohms. 1.0 megohms. 1,500 ohms.

20,000 ohms. 22.000 ohms.

... -do: 100,000ol1ms.

Capacitance... 0.01 microfarad. do. 0.1 microiarad.

0.35 inicrofarad. 1.0 mierofarad.

0.01 microfarad. 0.01 microiarad. 0.001 microfarad. 0.25 microfarad.0.25 microforad. 1.0 microfarad. 1.0 microfarad. 20 volts each side oftap 62. 12.6 v. to ground. 6.3 v. to ground. 115 volts to ground orterm- 111231 17. 220 volts D. C. with no load.

147 conductor) o 101 Econductor).. bias yoltage 1.5 volts. 165(conductor)...... uo 20.0 volts. 141 (conductor) ..do 42.0 volts.

Operation The temperature responsive network II on becoming unbalanceddue to a change in the temperature of the temperature responsiveresistance elements I8, I9 and 20 will produce a signal that is fed intothe amplifier I0 at the input terminal I2. This signal voltage will beamplified to control one or the other of the relays H15 and I45 tothereby effect energization of the motor I3 which will drive the value50 and the slider arm AI. Assuming that one of the temperatureresponsive resistances in the temperature responsive bridge network isenclosed in a chamber that is being heated by the medium that is passedthrough the valve 50, if the temperature inside the chamber drops to avalue lower than the control point that is set in the temperatureresponsive bridge, the amplifier I0 will cause rotation of the motor insuch a direction so as to increase the heat input to the chamber and atthe same time move the slider arm II in a direction to rebalance thebridge network II. As the temperature of the chamber increases and thebridge will again become unbalanced, in the opposite direction, a signalwill be produced on the input of the amplifier to effect rotation of themotor in the opposite direction to reduce the flow through the valve 50and also move the slider arm 4| in the opposite direction to produce abalanced condition in the bridge network II. By means of the variableresistance element 28 in the bridge network II it is possible to selecta desired control point. By means of the variable resistance element 20and the wiper arm 3|, the sensitivity of the resistance element 30 canbe increased or decreased. This sensitivity adjustment not only providesfor a greater or less movement in the position of the slider arm 41 butalso provides for an adjustment as to the maximum and minimum range ofoperation of the valve 50 at a given unbalance of the temperatureresponsive bridge II.

In first considering the details of the invention the amplifier will beexplained with the conductor I65 disconnected from the power supply I00.Let us assume that the temperature responsive bridge I I becomesunbalanced in one direction and a signal of a given magnitude and phaserelation is impressed on the amplifier at the input terminal I2. Thesignal is amplified by means of the first, the second, and the thirdstages of amplification in a conventional manner. Referring to Figure 2,sub-section A, the curve M is a graphical representation of the voltagethat is impressed on the third stage of amplification I2 at the controlelectrode I I2. The grid voltage wave M is shown to be biased above thecutoiI voltage J of the triode I10 by the distance 0 and the positivecycle of the grid voltage wave M is shown not to exceed the distance P,therefore, at no time does the grid voltage wave M produce a positivebias on the grid or pass below the cutofi voltage J of the triode I I0.In section B, of Figure 2, the voltage output wave of the triode H0 isshown as the curve N. It is, therefore, obvious that the A. C. componentof the output from the third stage of amplification will be impressed onthe input of the discriminator stage through the coupling capacitor I30. The voltage that is present on the control electrodes I29 and I32 ofthe discriminator stage I3 is shown in section 0, of Figure 2, as thevoltage curve Q. In the section C, the curve designated as R representsthe alternating reference voltage that is impressed on one of thecathodes of the discriminato'r stage 13 by the primary winding 59 of thetransformer 56. Assuming that the curve R is the voltage on the cathodeI30 of the first section of the discriminator tube I2! and the voltagewave Q as stated before is the voltage on the control electrode I29 ofthe same section. When the voltage wave Q is positive with respect tothe voltage wave R, the first section of the discriminator tube willconduct current from the power supply I44 through the relay assembly I45and through the first section of the discriminator tube I2'I. In sectionE, of Figure 2, the wave form F represents the current output of thefirst section of the discriminator tube I27. While it is not shown insection C of Figure 2, the anode voltage for the anode I28 of the firstsection of the discriminator tube I2! is at a positive unidirectionalpotential that is obtained from the power supply I44 as stated before inthe specification.

The problems associated with back emission, commonly known to be theelectron now from the anode to the control electrode of an electronicdischarge device, are frequently present when the anode potential of anelectronic discharge tie vice becomes negative with respect to thecontrol electrode. In a phase discriminator circuit, back emission oftenresults in a changing of the bias voltage of the input circuitcomprising the two control electrodes of the discriminator tube suchthat the input signal is less effective. In the discriminator stage ofthis invention the anodes I28 and I 3| of the discriminator tube aremaintained at a positive D. C. potential. Therefore,- at no time doesthe potential of the control electrodes become more positive than theanode potential and no back emission can exist.

Common to all phase discriminator circuit is the need of a referencevoltage. In this invention the two cathodes of the discriminator tubeare connected to the end terminals of a transformer having the centertap that is grounded so that the reference voltage is applied to thecathodes.

The operation when the conductor IE5 is connected to the power supply weat the junction of the resistors ISI and I62 will now be con-' sidered.This connection provides for applying a negative bias to the controlelectrode of the third stage of amplification 72 when either of therelay assemblies I45 or hit is energized. Assuming that the relayassembly I45 is energized as a result of the discriminator tube currentand the movable blade I'll makes contact with the contact no, a circuitcan be traced from the power supply I c, through the conductor I65, thecontact assembly, conductor I553, and the resistor I9I to the junctionI25. This connection will cause an increase in the negative bias that isapplied to the control electrode II2 oi the triode IIIl. When theswitching action of the relay assembly I45 occurs, the negative biasdoes not change instantaneously on the control electrode II2, however,the capacitor H that is used as the coupling capacitor between thesecond and third stages of amplification provides an RC delay network inconjunction with the resistance I9I. Referring to the section A, ofFigure 2, the change of the negative bias P on the control electrode II2of the triode III] is shown by the curve T. It should be understood thatthe time constant of the RC network com prising the capacitor Hi5 andthe resistor I9I is much longer than that shown by the. curve T withrespect to the frequency of the voltage signal M, however, for purposesof explanation it 10 will be shown as occurring in a shorter time. Insection A, the curve U represents the grid voltage of the amplificationstage I2 and is obtained by the algebraic addition of the values of thevoltage curve M and the bias voltage shown by the curve T. In section Bthe curve V represents the output voltage of the amplifier stage 72which in turn reflects into the discriminator stage the grid voltagecurve W shown in section (3'. The action of the discriminator tubedepends upon the positive magnitude of the grid voltage curve W withreference to the voltage wave R that has been previously stated to bethe voltage on the cathode I 30 of the discrimihat-or tube I21. Insection E of Figure 2, the solid line curve designated as X representsthe output of the first section of the discriminator stage I3 as aresult of the changing bias action on the third stage of amplificationI2 that is shown in section A of Figure 2. In section E, of Figure 2,the distance K and L represents the magnitudes of the drop-out andpull-in current, respectively, of the relay assembly I45. Since thediscriminator tube only conducts during one half of the alternatingvoltage cycle the output of the first section of the discriminator stagewill be a half=wave pulsating current such as shown by the curve insection E of Figure 2.

The capacitor I83 that is connected in parallel with the relay windingI82 of the relay ass'en bly I45 charges when each pulse of current isobtained from the discriminator tube and discharges during the next halfcycle so as to maintain energization of the relay between the halfwavecurrent pulses. In section E, of Figure 2, the curve Y represents thecurrent in the relay winding I32 as a result of the charging anddischarging of the parallel connected capacitor. When the current Y inthe relay winding reaches a magnitude that is equal to the pull-incurrent of the relay assembly shown as L, the relay will operate. At thesame time that the relay opcrates as shown in section D the bias voltageas shown in section A, of Figure 2, will begin to change on the curve T.As the current pulses to the relay winding that are shown as the solidline curve X, in section B, become smaller and smaller the relayassembly will drop out when the current Y in the relay winding decreasesto a magnitude that is smaller than the drop out current K. When therelay drops out, the additional negative bias that is applied by thejunction of the conductor I65 to the power supply It") will bedisconnected from the control electrode II2 of the amplification stageI2. Since the capacitor I I 5 charged to a voltage value that is morenegative than that charge that would be obtained from the normal bias onthe control electrode the condenser will discharge through the circuitthat can be traced through the conductor I25, the resistor I28, and theconductor I lI to the power supply I60. The value of the resistor I25can be selected so that the time constant of the RC combination of thecapacitor H5 and the resistor I20 is of such a value to obtain a desirednull timing. lfhe discharging of the voltage bias on the controlelectrode II2 of the triode II 6 is shown in the section A, of Figure 2,by the voltage curve Z. While the curve U was shown to be an algebraicaddition of the voltage curve M and the bias voltage T, it is continuedas the algebraic addition of the same curve M and bias voltage Z. Asthe'grid voltage for the amplification stage 12 increases in a positivedirection on the voltage bias wave Z the output of the discriminatorsection will increase and the current pulses designated as curve X insection E, of Figure 2, will also increase. The relay current Y onexceeding the pull in current value L will cause operation of the relayand thus start a second operation of the same cycle previouslyexplained.

In the explanation of the operation of this circuit a particular signalvoltage to the third stage of amplification 12 was selected as shown insection A, of Figure 2, as the wave form M. It is obvious that if theunbalance of the bridge network H was greater the amplitude of the gridvoltage wave M would be increased. While an increased magnitude in thegrid voltage wave M would cause the grid to be positive on the triode Hand also on the negative cycle to go below the cutoff value of thetriode tube H0, it is also important to recognize that with thisincreased magnitude in the voltage curve M it would be possible that thelowering of the bias voltage as shown in the curve T would not lower thepositive swing of the grid voltage sufiiciently below the cutoff value.Therefore, the relay would not drop out until the bridge network ll hadbeen rebalanced sufiiciently to reduce the magnitude of the input signalto the triode H0. The cycling action that is obtained by applying thenegative bias to the control electrode H2 of the third stage ofamplification is shown to be ineffective if the input signal M hasmagnitude of such a value that the output current of the amplifier stage12 maintains an operational signal on the control circuit of thediscriminator stage 13.

The operation of the discriminator stage and the relay assembly has beenspecifically directed to one section of the discriminator stage and onerelay assembly. It should be understood that if the signal received fromthe bridge network II should be of the opposite phase, having anunbalance condition on the opposite side of the control point, the waveform that is shown in section A, of Figure 2, designated as curve M,would be reversed approximately 180 degrees. The same action would thentake place as explained before except with the reversed phase inputsignal and the relay assembly I46 would be controlled.

The intermittent operation of the discriminator circuit as previouslyexplained is known as an anti-hunting operation. When the bridge circuitH is extremely unbalanced a large signal is applied to the inputterminal [2 to cause operation of the motor in the output circuit,however, as the input signal is reduced the motor operatesintermittently in pulses which become shorter. This operation preventsovershooting or cycling about the control point. In this invention thisanti-hunt operation is accomplished by an improved and simplified meansrequiring two resistors I26 and I9! and the coupling capacitor I i whichalso connects the second and third stages of amplification.

While I have shown and described certain preferred embodiments of myinvention, modification will readily occur to those who are skilled inthe art, and I therefore wish my invention to be limited only by thescope of the appended claims.

I claim as my invention:

1. An electronic amplifier comprising in combination: an output stagehaving an input and an output circuit; a voltage amplification stagehaving an anode, a cathode, and a control electrode; a relay; circuitmeans connecting said anode to said input circuit and said outputcircult to said relay; a coupling capacitor; an input signal circuit; acircuit means connecting said input signal circuit through said couplingcapacitor to said control electrode; a source of unidirectional voltagesupply connected to said cathode and having a first tap at a potentialnegative with respect to said cathode and a second tap at a potentialeven more negative with respect to said cathode; a first circuitextending from the junction of said coupling capacitor and said controlelectrode to said first tap and including resistance means to form withsaid capacitor, a first resistance-capacitor circuit, said firstresistance-capacitor circuit normally being effective to bias saidvoltage amplification stage so that in the absence of an input signalsaid relay is not effectively energized; and a second independentconnection extending from the junction of said coupling capacitor andsaid control electrode to said second tap, said second connection beingcontrolled by said relay and effective only when said relay isoperatively energized to tend to increase the bias of said voltageamplification stage so as to tend to cause deenergization of said relayunless said signal is above a predetermined value, said secondconnection furthermore comprising resistance means but including none ofthe resistance of said first connection so that the time constant of thecircuit including said second connection is unaffected by the resistancein said first connection.

2. An electronic amplifier comprising in combination: an output stagehaving an input and an output circuit; a voltage amplification stagehaving an anode, a cathode, and a control electrode; a relay; circuitmeans connecting said anode to said input circuit and said outputcircult to said relay; a coupling capacitor; an input signal circuit;circuit means connecting said input signal circuit through said couplingcapacitor to said control electrode; a plurality of sources ofunidirectional biasing voltage connected to said cathode; a firstcircuit extending from the junction of said coupling capacitor in saidcontrol electrode to the first of said sources of biasing voltage andincluding resistance to form with said capacitor, a firstresistance-capacitance circuit, said first resistance-capacitancecircuit normally being effective to bias said voltage amplificationstage so that in the absence of an input signal said relay is noteffectively energized; and a second independent connection extendingfrom the junction of said coupling capacitor and said control electrodeto said second source of biasing voltage, said second connection beingcontrolled by said relay and efiective only when said relay isoperatively energized to tend to increase the bias of said voltageamplification stage so as to tend to cause deenergization of said relayunless said signal is above a predetermined value, said secondconnection furthermore comprising resistance means but including none ofthe resistance of said first connection so that the time constant of thecircuit including said second connection is unafiected by the resistancein said first connection.

3. An electronic circuit comprising in combination: an amplificationstage including a first and a second electronic discharge device eachhaving an anode, a control electrode, and a cathode, means for producingan electrical signal potential having a magnitude and a phasecharacteristic dependent on the magnitude and direction of the unbalanceof said means, said means being connected to the input circuit of saidamplification stage; an output stage having two anodes,

13 two control electrodes, and two cathodes; a source of irreversibleunidirectional potential; two current actuated devices; circuit meansconnecting said source through one of said current actuated devices tothe first of said two anodes and connecting said source through theother of said current actuated devices to the second of said two anodes;a source of alternating potential having two end terminals and a tap; acoupling capacitor; circuit means connecting said end terminals to saidtwo cathodes; circuit means connecting said anode of said firstelectronic discharge device through said capacitor to the controlelectrode of said second electronic discharge device; circuit meansconnecting said anode of said second discharge device to said twocontrol electrodes so that said amplification stage on receiving aselective signal having an amplitude above a first determined minimumvalue at the control electrode of said first electronic discharge devicewill selectively effect operation of one of said current actuateddevices; a plurality of sources of biasing voltage connected to saidcathode of said second discharge device; a first circuit extending fromthe junction of said coupling capacitor and said control electrode ofsaid second discharge device to the first of said sources of biasingvoltage and including resistance to form with said capacitor a firstresistance-capacitance circuit, said first resistance-capacitancecircuit normally being eifective to bias said amplification stage sothat in the absence of an input signal said current actuated devices arenot efiectively energized; and a second independent connection extendingfrom said junction to said second source of biasing voltage, said secondconnection being controlled by said current actuated devices andeffective only when one of said current actuated devices is operativelyenergized to tend to cause de-energization of said current actuatedmeans unless said signal potential exceeds a second predetermined value,said second connection furthermore comprising resistance means butincluding none of the resistance of said first connection so that thetime constant of the circuit including said second connection isunaffected by the resistance in said first connection.

4. An electronic amplifier comprising in combination: a discriminatorstage having two anodes, two control electrodes, and two cathodes; avoltage amplification stage having an anode, a cathode and a controlelectrode; a pair of relays; circuit means connecting the anode of saidamplification stage to said two control electrodes; a source ofirreversible unidirectional potential; circuit means connecting said twoanodes to said unidirectional source through said relays; a couplingcapacitor; an input signal circuit; circuit means connecting said inputsignal circuit through said coupling capacitor to said controlelectrode; a plurality of sources of unidirectional biasing voltageconnected to said cathode; a first circuit extending from the junctionof said coupling capacitor and said control electrode to the first ofsaid sources of biasing voltage and including resistance means to formwith said capacitor a first resistance-capacitance circuit, said firstresistance-capacitance circuit normally being effective to bias saidvoltage a mplification stage so that in the absence of an input signalsaid relay is not effectively energized;

and a second independent connection extending from said junction to saidsecond source of biasing voltage, said second connection beingcontrolled by said relays and effective only when one of said relays isoperatively energized to tend to increase the bias of said voltageamplification stage so as to tend to cause de-energization of said relayunless the signal is above a predetermined value, said second connectionfurthermore comprising resistance means but including none of theresistance of said first connection so that the time constant of thecircuit including said second connection is unaffected by the resistancein said first connection.

5. An electronic control device comprising in combination: adiscriminator stage having two anodes, two control electrodes, and twocathodes; an amplification stage; a source of signal potential; circuitmeans including said amplification stage for connecting said source tosaid two control electrodes; a source of irreversible unidirectionalpotential; a plurality of current actuated devices one or the other ofwhich it is desired to actuate depending on the phase of said signalpotential; circuit means connecting said source of unidirectionalpotential to said two anodes through said current actuated devices; asource of alternating biasing voltage; circuit means connecting said twocathodes to said source of biasing voltage for biasing saiddiscriminator stage to insure only one of said anode circuits conductsfor a given phase of signal voltage; and

means operable upon either of said current actuated devices beingenergized to change the potential applied to said control electrodes totend to de-energize said current actuated device.

6. An electronic control device comprising in combination: adiscriminator stage having two anodes, two control electrodes, and twocathodes; a source of signal potential; circuit means for connectingsaid source to said two control electrodes; a source of irreversibleunidirectional potential; a plurality of relays one or the other ofwhich it is desired to actuate depending on the phase of said signalpotential; circuit means connecting said source of unidirectionalpotential to said two anodes through said relays; a source ofalternating bias voltage; circuit means connecting said two cathodes tosaid source of biasing voltage for biasing said discriminator stage toinsure only one of said anode circuits conducts for a given phase ofsignal voltage; and means operable upon either of said relays beingenergized to change the potential applied to said control electrodes totend to de-energize said relay.

DOUGLAS W. RIVENBURG.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,801,657 Buyko a Apr. 21, 1931 2,150,440 Hargreaves Mar. 14,1939 2,224,119 Harrison Dec. 3, 1940 2,260,977 Jones Oct. 28, 19412,425,733 Gille Aug. 19, 1947 2,429,636 McCoy Oct. 28, 1947 2,434,822Van Beuren Jan. 20, 1948 2,478,203 McCoy Aug. 9, 1949 2,507,304Hofstadter May 9, 1950 2,556,556 Schmitt June 12, 1951 2,579,001 JeifersDec. 18, 1951

